Field of the Invention
The invention relates to a power conversion control technique, and more particularly, to a three-phase inverting apparatus and a control method and a paralleled power conversion system thereof.
Description of Related Art
Among green energy, solar energy is an inexhaustible energy. Techniques related to the solar energy are growingly developed. After the solar energy is obtained by a solar power-generation apparatus (e.g., a solar panel) and then converted into electricity, the electricity can be directly incorporated into a local distribution network or stored in batteries. However, the batteries relatively cost high due to limited lifespan thereof. In case an inverter is used, if the solar energy is directly incorporated into the local distribution network through the inverter, power consumption during transmission can be reduced, as well as power loss can be lowered down, which leads to higher efficiency of the power-generation system.
For the existing power conversion systems, reliability of the inverter is a very important factor in design considerations for realizing stable power supply and conversion. However, as restricted by unexpected influences such as working environment factors and control interferences, none of the inverter designs can absolutely guarantee that no failure will occur during operations. Further, in response to the trend towards the increasing load capacity, a power converter must also increase its own capacity in order to satisfy requirements in various applications.
To reduce risks of the power supply being stopped due to failure of the inverter, a power conversion system architecture formed by multiple inverters connected in parallel has been proposed in the existing applications, so that the other inverters can still operate when failure occurs on one of the inverters. However, in the existing paralleled power conversion systems, the issue of circulating current will generally occur due to inconsistent output currents from each of the inverters, resulting in an unstable system operation.
In addition, because an inductance of a three-phase inverter does not remain unchanged, the inductance will become smaller if the current is greater in the system with greater power. If a controller fails to take into account the inductance variation, it is bound to overcome the insufficient inductance by using extremely large amount of compensations, which lead to risks of oscillations or even divergence in the system.